[Assist] signature verification

[quiliro at riseup.net]

As per https://wiki.parabola.nu/Installation_Guide#Download , I have 
tryed signature verification. I get the following output:
$ pacman-key -v SHA512SUMS.sig
==> Checking SHA512SUMS.sig ...
gpg: no hay datos firmados
gpg: can't hash datafile: No data
==> ERROR: La firma identificada por SHA512SUMS.sig no pudo ser 
verificada.

On another issue, I get 404 Not Found on:
https://repo.parabola.nu/iso/mate/SHA512SUM

In summary, I do not understand how to use any of these:
SHA512 | GPG signature
WHIRLPOOL | GPG signature
GPG Signing Key
from https://wiki.parabola.nu/Get_Parabola